Why were Super Bowl anti-terrorism documents not encrypted?

According to CCN one of their employees discovered copies of sensitive DHS material, in the seat-back pocket of a commercial plane. The reports were accompanied by the travel itinerary and boarding pass of the government scientist in charge of BioWatch. Biowatch is the DHS program that conducted the anthrax drills in preparation for Super Bowl LII in Minneapolis.

The Department of Homeland Security documents critiquing the response to a simulated anthrax attack on Super Bowl Sunday was marked “For Official Use Only” and “important for national security.”